A reference scale of cucurbit[7]uril binding affinities.

The accurate determination of ultra-high binding affinities in supramolecular host-guest chemistry is a challenging endeavour because direct binding titrations are generally limited to affinities <10 M due to sensitivity constraints of common titration methods. To determine higher affinities, competitive titrations are usually performed, in which one compound with a well established binding affinity serves as a reference. Herein, we propose a reference scale for such competitive titrations with the host cucurbit[7]uril (CB7) comprising binding affinities in the range from 10 to 10 M. The suggested reference compounds are commercially available and will aid in the future determination of CB7 binding affinities for stimuli-responsive host-guest systems.